A cough is an abrupt, forceful ejection of air from the lungs. A cough is not only the single most frequent symptom for which patients seek medical care in the United States and around the world, but also one of the most perplexing and frustrating disease-provoking diagnostic challenges for the clinician. The purpose of a cough is to clear the airways and to protect them from inhaled foreign particles, such as pollen, dust, microbes, and others.

There are two types of coughs: dry cough (unproductive) and wet cough (productive). A productive cough often brings phlegm/sputum/mucus. The phlegm can be white, tan, yellow, green, or accompanied by streaks of blood. In some cases, a severe cough can result in straining of the rib muscles and cartilage, causing chest pain when breathing or moving. A cough can be bothersome, disrupting daily activities and interfering with sleep.

A cough occurs when bronchial airways are irritated by certain particles. A cough can be classified as an acute cough, known to last fewer than 3 weeks in adults and fewer than 4 weeks in children, or as a chronic cough, known to last more than 3 weeks in adults and more than 4 weeks in children.

1. Upper respiratory infection
2. Postnasal drip (mucus draining from the nose to the throat)
3. Activation of chronic obstructive pulmonary disease (COPD) with an infection (bronchitis)
4. Pneumonia (a lung infection caused by bacteria, virus, or fungi)
5. Heart failure
6. Pulmonary embolism (a blood clot in the lungs)
7. Foreign body (i.e., a piece of aspirated food)

A chronic cough is commonly triggered by one, or a combination of, the following:

1. Cough variant asthma (CVA), a type of asthma that only expresses itself by a cough.
2. Upper airway cough syndrome (UACS) (previously called postnasal drip syndrome), often triggered by nasal allergy and sinus disease.
3. Gastroesophageal reflux (GERD) or laryngopharyngeal reflux (LPR). This is a chronic digestive disorder that occurs when stomach acid (or even stomach content) goes up into the esophagus (food pipe). The acid backwashes the throat and then irritates the cough receptors, triggering a cough.
4. Irritation of the airways that lasts after a respiratory infection resolves.
5. Chronic bronchitis (especially in smokers).
6. Blood pressure medications called angiotensin-converting enzyme inhibitors (ACEI).
7. Pulmonary fibrosis, also called interstitial lung disease, consisting in progressive scarring of the lungs.
8. Cancer of the lungs.
9. Fungal infection of the lungs.
10. Tuberculosis.
11. Habit cough (psychogenic cough), a cough that may occur after a cold, leading to a vicious cycle (cough--throat irritation--cough), that typically stops once you fall asleep.
12. Bronchiectasis (damage of the airway).
13. Cystic fibrosis (inherited disorder causing severe airway damage).
14. Bronchiolitis (viral infection in infants and young children).
15. Sarcoidosis (collection of inflammatory cells in the lungs).

People with a cough should immediately seek medical attention if they experience one or more of the following symptoms, including, but not limited to:

1. Coughing up blood.
2. Difficulty breathing.
3. Cyanosis (bluish discoloration of the skin and/or lips due to poor oxygenation of the blood.
4. Fever lasting more than 7 days.
5. Risk factors for HIV (risky sexual activities, use of injectable street drugs).
6. Risk factors for tuberculosis (foreign travel to endemic areas).
7. Weight loss without dieting.

Experiencing a chronic cough can be exhausting, and can disrupt your daily activities and sleep patterns. It can also cause or exacerbate the following:

1. Dizziness.
2. Incontinence (loss of bladder control).
3. Headaches.
4. Sweating.
5. Fracture of ribs.
6. Syncope (passing out).